Limits
All 'systems', whether natural or artificial, possess limitations as to their function and ability to resist or accomodate external influences. Exceed those limitations and the system will fail or adapt. A natural system, such as the Earth's climate, adapts but the changes this process produces are not necessarily compatible with the biological lifeforms that rely upon it or, they may occur faster than these reliant systems can themselves adapt.
In human terms this simply means that the changes to the Earth's climate we have triggered, by our persistant and abusive use of the Earths natural resources, may make it difficult for many of the Earth's species to survive, including humanity. Whilst this will be catastrophic for our species, in the universal scheme of things, it will mean nothing.